Polyamides, represented by polyamide 6, polyamide 66 (hereinafter sometimes respectively abbreviated as “PA6” and “PA66”), and the like, have good fabricability, mechanical properties and chemical resistance, and are hence widely used as various component materials for automobile, electric and electronic products, industrial materials as well as daily and household products, and the like.
In the automotive industry, there is a demand to lighten the car body weight using a metal substitute material for the purpose of achieving the exhaust gas reduction as a countermeasure against environmental issues. To respond to such a demand, polyamide materials have been commonly used as exterior materials, interior materials, or the like, which consequently requires much higher levels of properties of polyamide materials such as heat resistance, strength, appearance, and the like. In particular, the temperature in the engine room is likely to elevate, and accordingly highly heat resistant polyamide materials have been in an increasing demand.
Further, in the electric and electronic industry for household electric appliances and the like, there is a demand for highly heat resistant polyamide materials which are resistant to an increased soldering melting point in order to meet the lead-free soldering surface mount technology (SMT).
However, the polyamides such as PA6 and PA66 described earlier have low melting points and hence fail to meet these requirements in the heat resistance.
To solve the problems of heat resistance posed by the conventional polyamides such as PA6 and PA66, high melting point polyamides have been proposed. Specifically, a polyamide composed of terephthalic acid and hexamethylenediamine (hereinafter, sometimes abbreviated as “PA6T”), and the like, are proposed.
However, PA6T is a high melting point polyamide having a melting point of about 370° C. and causes notable thermal decomposition of the polyamide when producing a molded product by the melt process which consequently makes it difficult to obtain a molded product that has sufficient properties.
To solve the problem of thermal decomposition of PA6T, proposed are high melting point semi-aromatic polyamides mainly composed of terephthalic acid and hexamethylenediamine which are allowed to have a melting point as low as about 220 to 340° C. by copolymerizing PA6T and aliphatic polyamides such as PA6 and PA66, or a noncrystalline aromatic polyamide composed of isophthalic acid and hexamethylene diamine (hereinafter sometimes abbreviated as “PA6I”), or the like, (hereinafter sometimes abbreviated as “PA6T copolymer”), and the like.
As the PA6T copolymer, Patent Document 1 discloses an aromatic polyamide composed of aromatic dicarboxylic acid and aliphatic diamine, which is a mixture of hexamethylenediamine and 2-methylpentamethylenediamine (hereinafter sometimes abbreviated as “PA6T/2 MPDT”).
In addition to the aromatic polyamide composed of an aromatic dicarboxylic acid and an aliphatic diamine, a high melting point aliphatic polyamide composed of adipic acid and tetramethylenediamine (hereinafter sometimes abbreviated as “PA46”), an alicyclic polyamide composed of an alicyclic dicarboxylic acid and an aliphatic diamine, and the like, have been proposed.
For example, Patent Documents 2 and 3 disclose semi-alicyclic polyamides composed of an alicyclic polyamide composed of 1,4-cyclohexane dicarboxylic acid and hexamethylenediamine (hereinafter sometimes abbreviated as “PA6C”), and another polyamide (hereinafter sometimes abbreviated as “PA6C copolymer”).
Patent Document 2 discloses that electric and electronic components made of a semi-alicyclic polyamide containing 1 to 40% of 1,4-cyclohexane dicarboxylic acid as the dicarboxylic acid unit have improved solder heat resistance, and Patent Document 3 discloses that automobile components made of a semi-alicyclic polyamide have good fluidity, toughness, and the like.
Patent Document 4 discloses that the polyamide composed of a dicarboxylic acid unit containing 1,4-cyclohexane dicarboxylic acid and a diamine unit containing 2-methyl-1,8-octane diamine has good light resistance, toughness, moldability, lightness, heat resistance, and the like. This document also discloses a method for producing such a polyamide, in which 1,4-cyclohexane dicarboxylic acid and 1,9-nonanediamine are reacted at 230° C. or less to prepare a prepolymer, which is then subjected to solid phase polymerization at 230° C. to produce a polyamide having a melting point of 311° C.
Further, Patent Document 5 discloses that the polyamide, which uses as a raw material 1,4-cyclohexane dicarboxylic acid having a trans/cis ratio from 50/50 to 97/3, has good heat resistance, low water absorbance, light resistance, and the like.
Patent Document 6 discloses that, in the production of a polyamide composed of a diamine component containing an aromatic diacid containing terephthalic acid and 2-methylpentanediamine, the cyclization of 2-methylpentamethylenediamine (a cyclic amino group is formed) is significantly reduced by adding formic acid.
Further, Patent Documents 7 and 8 disclose that, in a polypentamethylene adipamide resin, when the bonding of a cyclic amino group derived from pentamethylenediamine to a polymer end is reduced by controlling the polymerization temperature, and the like, the residence stability and heat resistance of the polyamide can be improved.
Furthermore, Patent Document 9 describes the polyamide obtained by polymerizing a dicarboxylic acid containing an alicyclic dicarboxylic acid and a diamine containing a diamine having a substituent branched from the main chain.